Searching for a Bacteriophage Lysin to Treat Corynebacterium bovis in Immunocompromised Mice

Corynebacterium bovis is the causative agent of Corynebacterium-associated hyperkeratosis in immunocompromised mice. The resulting skin pathology can be profound and can be associated with severe wasting, making the animals unsuitable for research. Although the administration of antibiotics is effective in resolving clinical symptoms, antibiotics do not eradicate the offending bacterium. Furthermore, antibiotic use may be contraindicated as it can affect tumor growth and is associated with Clostridioides difficile enterotoxemia in highly immunocompromised murine strains. Lysins, which are lytic enzymes obtained from bacteriophages, are novel antimicrobial agents for treating bacterial diseases. The advantage of lysins are its target specificity, with minimal off-target complications that could affect the host or the biology of the engrafted tumor. The aim of this study was to identify lysins active against C. bovis. Chemical activation of latent prophages by using mitomycin C in 3 C. bovis isolates did not cause bacteriophage induction as determined through plaque assays and transmission electron microscopy. As an alternative approach, 8 lysins associated with other bacterial species, including those from the closely related species C. falsenii, were tested for their lytic action against C. bovis but were unsuccessful. These findings were congruent with the previously reported genomic analysis of 21 C. bovis isolates, which failed to reveal bacteriophage sequences by using the PHAST and PHASTER web server tools. From these results, we suggest C. bovis is among those rare bacterial species devoid of lysogenic bacteriophages, thus making the identification of C. bovis-specific lysins more challenging. However, C. bovis may be a useful model organism for studying the effects of antiphage systems.

[Phage resistance of Corynebacterium crenatum conferred by the restriction and modification system cglI]

In order to prevent phage contamination in amino acid fermentation, we introduced the restriction and modification system cglI gene complex into Corynebacterium crenatum and studied their phage-resistance. The cglI gene complex was amplified from Corynebacterium glutamicum by PCR and constructed into pJL23 vector. The recombinant strains were obtained by transformation of the recombinant plasmid pJL23-cglI into C. crenatum. Results showed that the recombinant strains possessed strong phage-resistance activity and broad phage-resistance spectrum, demonstrating the feasibility of using cglI gene complex for construction of phage-resistance recombinant C. crenatum strains and presenting a powerful way to solve the problem of phage contamination in amino acid fermentation industry.

Properties of corynephage attachment site and molecular epidemiology of Corynebacterium ulcerans isolated from humans and animals in Japan

Sporadic reports of Corynebacterium ulcerans infection in humans and animals have become increasingly common throughout the world. Between 2001 and 2006, five human cases, in addition to isolation of the bacterium from the carcasses of Orcinus orca and Panthera leo, were reported in Japan. While an isolate from P. leo generated only phospholipase D (PLD), the other isolates produced both PLD and diphtheria-like toxin (DLT). Pulsed-field gel electrophoresis analysis showed that isolates from P. leo and humans were genetically homologous. Southern blotting found that a human isolate was lysogenized by two corynephages coding DLT. Sequence analysis of the region of the DLT gene revealed that the integration in C. ulcerans occurred in the same manner as that in C. diphtheriae.

Bacteriophage-based vectors for site-specific insertion of DNA in the chromosome of Corynebacteria

In Corynebacterium diphtheriae, diphtheria toxin is encoded by the tox gene of some temperate corynephages such as beta. beta-like corynephages are capable of inserting into the C. diphtheriae chromosome at two specific sites, attB1 and attB2. Transcription of the phage-encoded tox gene, and many chromosomally encoded genes, is regulated by the DtxR protein in response to Fe(2+) levels. Characterizing DtxR-dependent gene regulation is pivotal in understanding diphtheria pathogenesis and mechanisms of iron-dependent gene expression; although this has been hampered by a lack of molecular genetic tools in C. diphtheriae and related Coryneform species. To expand the systems for genetic manipulation of C. diphtheriae, we constructed plasmid vectors capable of integrating into the chromosome. These plasmids contain the beta-encoded attP site and the DIP0182 integrase gene of C. diphtheriae NCTC13129. When these vectors were delivered to the cytoplasm of non-lysogenic C. diphtheriae, they integrated into either the attB1 or attB2 sites with comparable frequency. Lysogens were also transformed with these vectors, by virtue of the second attB site. An integrated vector carrying an intact dtxR gene complemented the mutant phenotypes of a C. diphtheriae DeltadtxR strain. Additionally, strains of beta-susceptible C. ulcerans, and C. glutamicum, a species non-permissive for beta, were each transformed with these vectors. This work significantly extends the tools available for targeted transformation of both pathogenic and non-pathogenic Corynebacterium species.

Complete nucleotide sequence and genome analysis of bacteriophage BFK20 — A lytic phage of the industrial producer Brevibacterium flavum

The entire double-stranded DNA genome of bacteriophage BFK20, a lytic phage of the Brevibacterium flavum CCM 251--industrial producer of L-lysine--was sequenced and analyzed. It consists of 42,968 base pairs with an overall molar G + C content of 56.2%. Fifty-five potential open reading frames were identified and annotated using various bioinformatics tools. Clusters of functionally related putative genes were defined (structural, lytic, replication and regulatory). To verify the annotation of structural proteins, they were resolved by 2D gel electrophoresis and were submitted to N-terminal amino acid sequencing. Structural proteins identified included the portal and major and minor tail proteins. Based on the overall genome sequence comparison, similarities with other known bacteriophage genomes include primarily bacteriophages from Mycobacterium spp. and some regions of Corynebacterium spp. genomes--possible prophages. Our results support the theory that phage genomes are mosaics with respect to each other.

Resistance of corynebacterial strains to infection and lysis by corynephage BFK 20

AIMS

Defence mechanisms of the corynebacterial strains against corynephage BFK 20, which causes lysis of Brevibacterium flavum CCM 251.

METHODS AND RESULTS

We tested adsorption of the phage BFK 20 to the corynebacterial cell surface. We observed strong adsorption ranging from ca 79 to 93% on the cells of B. flavum ATCC strains, but only ca 76% for B. flavum CCM 251. Minor adsorption for Brevibacterium lactofermentum BLOB (ca 13%) and no adsorption for Corynebacterium glutamicum RM3 were determined. BFK 20 infection had no significant effect on growth and viability of C. glutamicum and B. lactofermentum, but significantly influenced growth and viability of B. flavum ATCC 21127, 21128 and 21474. Cell growth stopped in short time after infection but with no lysis. Brevibacterium flavum CCM 251 cell growth was arrested too and lysis occurred. The Southern hybridization confirmed the presence of significant amount of BFK 20 DNA in samples from B. flavum CCM 251 and B. flavum ATCC strains after BFK 20 infection. Only weak hybridization signal was detected for DNA from infected cells of B. lactofermentum BLOB and no signal for C. glutamicum RM3.

CONCLUSIONS

Based on the above results we suggest presence of a mechanism leading to abortive infection in B. flavum ATCC 21127, 21128 and 21474. In B. lactofermentum BLOB and C. glutamicum RM3 the adsorption barrier is more likely.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study increases the knowledge on defence mechanisms of corynebacteria against bacteriophages.

Fractionation of Corynebacterium pekinense AS 1.299 phage subtypes by anion-exchange chromatography

A novel method to fractionate phage into its subtypes while fully retaining biological function is reported. Corynebacterium pekinense AS 1.299 phage samples, purified by either conventional ultracentrifugation or gel chromatography on a Superose(R) 6 Prep column (0.78 x 30 cm), were fractionated further into four fractions by anion-exchange chromatography on a Toyopearl SuperQ 650C column (0.5 x 20 cm) with a linear gradient of NaCl concentration from 0.2 to 1.0 M in 0.02 M carbonate-biocarbonate buffer, pH 10.0. Two peaks were identified to be C. pekinense AS 1.299 phages by their ability to infect the host bacteria when inoculated into the culture media, and when examined by electron microscopy. These two types of the phage were found to be morphologically the same except for the difference in the length of their non-contractile tails. Both possessed an isometric head with a diameter of 50 +/- 3 nm, while their tails were 170 +/- 10 and 210 +/- 10 nm, respectively. This simple technique provides a convenient method for phage isolation not only to its species homogeneity, but also to determine its subtype or variant homogeneity.

Site-specific integration of corynephage phi16: construction of an integration vector

Phi16, a temperate phage induced from Corynebacterium glutamicum ATCC 21792, lysogenizes its host via site-specific recombination. The phage attachment site, attP, was located to a 6.5 kb BamHI fragment of the phi16 genome. This fragment also contained phi16 integrative functions. The minimal phage DNA fragment required for integration was defined. This 1630 bp region contained a large open reading frame, int, encoding a protein of 416 amino acids with similarity in its carboxyl-terminal domain to tyrosine recombinases and particularly to the Xer recombinases. The comparison of the nucleotide sequences of attB, attL, attR, and attP identified a common 29 bp sequence, the core sequence. It lies 11 bp downstream of the 3' end of the integrase gene. phi16 integrase was shown to catalyse site-specific integration in trans to attP with an efficiency of 5x10(3) integrants per microg DNA. The integrating fragment catalysed integration in several Corynebacterium strains that are not infected by phi16, thus enlarging the host spectrum of integrating vectors derived from phi16. In these strains, the phi16 attB site was located in a conserved intergenic region and lies downstream of a clp gene.

Extended host range of a beta-related corynebacteriophage

Unlike most beta-related phages isolated from Corynebacterium diphtheriae, phage 782 readily plaqued on strains of C. ulcerans and C. pseudotuberculosis. The extended host range of phage 782 was not, however, due to a greater ability of the phage to absorb to bacterial surfaces. Using chemical mutagenesis, a number of phage mutants were isolated which had diminished capacities to infect C. ulcerans, suggesting the existence of a locus (ehr) for extended host range. Pre-lysogenization of C. ulcerans strains with phage 782, but not its mutant form or other beta-related phages, rendered them susceptible to infection by previously excluded phages. An examination of recombinant between phages 782, pie, and beta localized ehr to a 7 kilobase region of DNA including attP. The data are compatible with the notion that ehr encodes an anti-restriction function.

Prophage distribution in coryneform bacteria

Four temperate bacteriophages of corynebacteria were isolated after UV induction. Phages phi 304L and phi 304S were both induced from Corynebacterium glutamicum ATCC 13058, ATCC 21488, ATCC 21649 and ATCC 21650 strains, and have no known sensitive host. Phages phi 15 and phi 16 were both induced from ATCC 14020 and ATCC 21792. Phage phi 15 formed turbid plaques on Corynebacterium sp. ATCC 21857 and on C. glutamicum ATCC 13058, ATCC 21488, ATCC 21649 and ATCC 21650. Phage phi 16 produced turbid plaques only on C. glutamicum ATCC 21792 cured of prophage phi 16. All these phages belong to the Siphoviridae family. Their genomes consist of a double-stranded DNA with cohesive ends and share no homology with each other. Prophages phi 16, phi 304L and phi 304S were integrated into their respective host chromosomes, whereas prophage phi 15 seemed to persist free in the cell. Cross-hybridizations between phage DNAs and total cellular DNA obtained from 20 strains belonging to the genera Corynebacterium and Brevibacterium did not show the presence of these prophages in strains other than their respective hosts.

Characterization and sequence analysis of the F2 promoter from corynephage BFK20

F2 promoter from corynephage BFK20 was isolated and characterized. It was functional in Escherichia coli and Corynebacterium glutamicum. Cloning of the F2 promoter into the pJUP05 promoter probe vector caused an increase of the neomycin phosphotransferase II specific activity. According to the Northern blot hybridization the nptII gene was expressed from the cloned F2 promoter. The apparent transcription start point in E. coli and C. glutamicum was determined. The -35 region of F2 promoter showed high similarity to that of E. coli promoter consensus sequence, but its -10 region was G+C rich and had no significant homology to that.